Remove duplicated 'compression' documentation from googlecloudexporte…

…r readme (#28643)

The `compression` metric option appears more than once in the readme for
the googlecloudexporter exporter, so I've deleted one of the copies. The
first copy has more detail, so I preserved that one.

exporter/googlecloudexporter/README.md

@@ -192,7 +192,6 @@ The following configuration options are supported:
     - `regex`: Match resource keys by regex.
   - `cumulative_normalization` (default = true): If true, normalizes cumulative metrics without start times or with explicit reset points by subtracting subsequent points from the initial point. It is enabled by default. Since it caches starting points, it may result inincreased memory usage.
   - `sum_of_squared_deviation` (default = false): If true, enables calculation of an estimated sum of squared deviation.  It is an estimate, and is not exact.
-  - `compression` (optional): Enable gzip compression for gRPC requests (valid vlaues: `gzip`).
   - `experimental_wal` (default = []): If provided, enables use of a write ahead
     log for time series requests.
     - `directory` (default = `./`): Path to local directory for WAL file.